LED lighting devices are quickly replacing the once-ubiquitous incandescent bulbs. There are many advantages to LED lighting devices: for example, LEDs are longer lasting and offer a higher lumen output while using less power than traditional incandescent bulbs. Further, LED lighting devices offer a wide array of possible color temperatures, allowing a user to customize the feel his or her living space or other lighted area. For example, a user may employ a 2700K LED lighting device, offering a warm color temperature, for a comfortable setting. Or a user may use a 6500K LED lighting device, offering a bright color temperature, where bright, clear light is needed, such as for a commercial display.
Often it is desirable to adjust the color temperature of a single lighting device to emit a warmer or cooler color temperature, at any given time. Such a lighting device may be useful for tuning the light of the environment to the match the current daylight. For example, the lighting device may produce bright cool light during midday and warm light during early mornings and evenings.
However, a typical lighting device that can offer both warm and cool colors often requires an isolation power supply along with two LED drivers on the secondary side. In this scenario, there is a total of three power stages, which is complicated, expensive, and lumen inefficient. For example, if the specification requires a total output power of 50 W, a typical design would be 200 W driver (50 W for PFC/another 50 W for DC-DC and 100 W for the two LED drivers). The total power would be 50 W+50 W+100 W=200 W. (Some designs utilize a single stage AC-DC PFC that is integrated PFC and DC-DC into 1 power stage. With such designs, the total power will be 50 W+100 W=150 W). The power conversion system total efficiency is a multiplicative of each power stage. Thus, if a three stage power conversion topology is employed and the power conversion efficiency of each stage is 90%, then the system efficiency will be 72.9%. Further, controlling the lumen output of a variety of LEDs (or LED strings), each having a unique color temperature, generally requires multiple controller channels, which is costly and bulky.
Accordingly, a need exists in the art for a lighting control circuit that may control a variety of LEDs without the need for an LED driver for each LED, and that only uses a single current source for different LED channels via proper multiplexing and control.